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What are the 5 Main Branches of Physics?

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Updated: February 28, 2024, Reading time: 8 minutes

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As a broad and all-encompassing field, physics goes deeper into the study of matter and energy and how they interact by dividing the subject into various branches. These branches have evolved, focusing on the specific underlying aspects of the physical world. Each of the branches is equally important in the world at large. 

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Exploring the impact of physics often involves the need to understand its different branches within science, along with its wide range of principles and methodologies. Each branch has its name and objectives.

By understanding the branches and how they relate and differ from each other, aspiring physicists will be able to weigh their options and pursue a specialization that will lead them closer to the realization of their goals, helping them achieve career growth and fulfillment in the process.  

Grad School Center is an advertising-supported site. Featured or trusted partner programs and all school search, finder, or match results are for schools that compensate us. This compensation does not influence our school rankings, resource guides, or other editorially-independent information published on this site.

The 5 Main Branches of Physics

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Classical Mechanics

Classical Mechanics is by far the oldest branch of physics, and while this sub-field is best expressed in the Laws of Motion set forth by Sir Isaac Newton (and also draws on the work by scientists such as Hamilton, LaGrange, Euler, and others), the earliest work in this field dates back thousands of years, to the time of antiquity. 

In broad strokes, Classical Mechanics deals with the motion & dynamics of objects (or, more appropriately, bodies) under the influence of forces. Classical mechanics is most applicable to macro-scale objects, i.e., objects readily visible to the naked eye, spanning the scale of everyday objects right up to the stars and galaxies.

Classical mechanics is also applicable to what can be termed as everyday conditions, i.e., speeds of bodies are far lower than the speed of light. Other branches of physics start to be more applicable as we go to smaller and smaller scales (atoms and individual subatomic particles) and as speeds approach the speed of light.

Relativistic Mechanics

The branch of Relativistic Mechanics belongs to the group of branches collectively placed under Modern Physics, which took root around the start of the 20th century. It is anchored on Albert Einstein’s theories of General Relativity and Special Relativity. 

General Relativity contains the theory of gravitation first put forward by Albert Einstein in the early 1900s, while Special relativity is concerned with the relationship between mass, energy, space, and time. The two theories are interrelated, with General Relativity factoring gravity into the relationship between mass and energy and reframing the classical conception of gravity from that of an invisible pulling force into an effect of mass bending space and time. 

Thermodynamics

Thermodynamics is primarily concerned with the interrelationship between heat/temperature, energy, and work and their implications on the physical properties of matter. Thermodynamics looks at how thermal energy is transformed from and into other forms of energy. 

Thermodynamics is anchored on its four basic laws (named the zeroth, first, second, and third laws). The zeroth law governs the principle of equilibrium, while the first law governs the conservation of energy (energy cannot be created nor destroyed).

The second law governs the concept of entropy, or disorder/randomness in a system, while the third law governs the relationship between entropy and temperature (a system approaches zero entropy as it is theoretically cooled to absolute zero).

In more practical terms, while Einstein’s theories of relativity demonstrate the physical impossibility of faster-than-light travel, the laws of thermodynamics demonstrate the impossibility of perpetual motion machines (and therefore free unlimited energy). 

Electromagnetism

The branch of Electromagnetism focuses on the phenomena of electricity and magnetism and how the two are interrelated. The branch grew out of seminal work done during the eighteenth and nineteenth centuries by various researchers include Ampère, Coulomb, Faraday, Maxwell, and many others.

Before then, much of people’s efforts were centered on understanding readily observable electric phenomena, such as lightning, static electricity, and objects that exhibited magnetic properties. 

Electromagnetism is concerned primarily with the dynamics that occur between particles that possess an electric charge, in particular, their movement. Classical electromagnetism is anchored on a set of fundamental equations (known as Maxwell’s Equations) that describe the relationships between electric charges and electric currents with electricity and magnetic fields, together with Lorentz force law, which governs the combination of electric and magnetic force.

The discoveries in electromagnetism built progressively on the discoveries made by dozens of individuals and helped usher in the Second Industrial Revolution, which saw the proliferation of electricity-driven industrial processes. Discoveries in the field remain highly relevant, especially in light of our modern world, which is built on the foundation of electronic systems.  

Quantum Mechanics

The branch of quantum mechanics is the branch of physics that takes over from classical mechanics as we approach the atomic and sub-atomic scales. Quantum mechanics in its current form can be traced back to work done in the early 1900s, arising out of observations that were unreconcilable with the prevailing classical physics principles.

Some notable names in this field include Planck, Schrödinger, Bohr, Dirac, Heisenberg, and many others.

Given that many classical laws of physics seem to get overturned at the quantum scale, this branch has a reputation for being the hardest in Physics, though many would readily disagree.

Nevertheless, quantum mechanics and all its sub-branches, like quantum chemistry, quantum field theory, & quantum technology, represent the cutting edge of current research and are seen as the source of the next great technological leaps forward in many areas.

Other Branches of Physics

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Optics and Acoustics

Often referred to as acousto-optics, this particular brand of physics deals with the study of sound waves and light waves and how the two interact. Acoustics primarily deals with sound and everything it encompasses, including the production, control, transmission, reception, and possible effects.

While it involves the study of musical instruments and architectural spaces, acoustics also explores a wide range of topics such as thermoacoustic, seismology, ultrasounds for medical imaging, and electroacoustic communication. 

Optics, on the other hand, is a branch of physics that studies electromagnetic radiation, such as infrared radiation and light. It also covers its interactions with matter and the instruments being used to gather information from these interactions. This branch also delves into the study of sight. As the science of light, optics have influenced a variety of technological tools, from digital cameras and wireless mouse to Blu-ray discs. 

Condensed Matter Physics

This branch of physics specifically tackles the macroscopic and microscopic properties of matter. It studies the way matters arise from a large number of interacting atoms and electrons. Considered one of the largest subfields of physics, condensed matter has led to various breakthroughs, including the discovery and use of liquid crystals and composite materials. 

Physicists who specialize in this field explore the theoretical models of condensed matter. They are also expected to experiment and observe the behaviors of condensed matter, often done in laboratories. In the modern age, the study of condensed matter extended to innovative topics such as nonlinear optics, organic semiconductors, superconductivity, and polymer dynamics, among others. 

Nuclear Physics and Particle Physics

Straddling the boundary between physics and chemistry, Nuclear Physics is concerned with studying atomic nuclei and the way they interact, along with their formation and stability. This includes exploring interactions such as nuclear fusion and fission, and radioactive decay. 

This branch of physics has led to many innovations and enabled a range of new technologies. One of its biggest contributions is the application of nuclear physics in generating power. It has also left impacts in the field of healthcare, particularly in testing and treating cancer. Many advancements in medicine, materials, energy, and climatology can be traced back to nuclear physics. 

Particle physics focuses on the study of nature’s constituents and interactions, particularly at its most fundamental level. It grew out of the study of nuclear physics, exploring the elementary building blocks of matter, radiation, and their interaction. 

Astronomy 

The study of the universe beyond the atmosphere of the earth—the sun and the moon to the planets and the stars—is called astronomy. It also covers objects that cannot be seen by the naked eye, such as faraway galaxies and tiny particles. 

Under this branch, one will also find astrophysics, which is the study of how objects interact with each other across the universe. Astrophysics tackles electromagnetism, particle physics, gravitational force, and thermodynamics.


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